As sometimes happens when searching the net for information on one subject you find answers for a totally different problem.
I had always used electrical tape on the lens barrel to prevent my zoom's from creeping.This particular site showed how to tighten the barrel using Teflon or plumbers tape.Here's how:#1.Roll back the rubber lens grip to view the 2 screws set in in plastic holders.
#2.Remove one screw and plastic washer and wrap it in a small bit of Teflon tape then replace it.
#3.Repeat for the other set.
NOTE:Remove only one screw at a time.

Just finished tweaking my new 70-210 smc Pentax glass and it works like a charm.